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Traffic Noise Model: Frequently Asked Questions FAQs

Menu: Contours

  1. When I tried to calculate a contour of sound levels, NMPlot outputs an "invalid floating point error" and then halts contour calculations. What is causing this?

    There are a number of input errors that may cause this:

    1. It is an error encountered in your geometry. Change any point of your contour zone slightly (0.305 meters [1 ft.] will do) and recalculate the contour sound levels.
    2. The built-in version of NMPlot is a DOS program, so it cannot understand long file names, long folder names, or names with "spaces" and other DOS-illegal characters in them. To properly run noise contours, the path name must satisfy DOS's maximum of 8.3 characters and DOS's restriction against some characters (such as "spaces"). For example, 12345678.123 is a valid file name. Therefore, users must save their run in a folder directly on the C: drive and also keep their run and contour names to a minimum number of characters.
    3. You must also have a "barrier design" in your run. To create a barrier design, select your desired barrier and receivers with the mouse, and then click on Barrier Analysis->New. A new "Barrier View" will open. If you want the contours to be generated for a barrier set at the input height, then click on Barrier Analysis->Remember As. Here you can type in a name for your barrier design, click OK and it is saved. You can then exit out of the "Barrier View," select the contour you wish to calculate, and click on Contours->Define Contour Levels. Input your contour level data and then click on Contours -> Calculate. You will now be prompted to select a barrier design, and the one you just created will be included in the list. Select it and contours will begin calculating. If there are no other problems with the run, this will generate contours for your run.
  2. In Version 1.1: I took care of the "Out of Memory" problem, but now when I run NMPlot, I receive a FATAL ERROR message about the file format created by Noisemap not being the one expected by NMPlot. I had already downloaded NMPLOTX.EXE Version 3.06, so I don't think that's the problem. Is this something fixed in Version 2.0?

    (Applies to TNM versions 1.1 and 2.0 only)
    Some TNM 1.1 users are experiencing problems computing contours. We do not recommend using Version 1.1 to generate contours, but instead use Version 1.0b or TNM 2.0 and higher. TNM Version 2.0 has addressed many issues in calculating contours. Also, remember when calculating with contours that NMPlot is a DOS application with an 8-character filename/directory limit. If your TNM run name is greater than 8 characters or is embedded within many subdirectories or has long subdirectory names, then NMPlot may display errors. Shorten your run name or move your run out to the main C: directory to run contours.

  3. Are contours allowed to intersect other TNM objects?

    While contour zones can intersect other TNM objects, users should be advised not to intersect or encompass roadways and barriers with contour zones, because contouring logic can break down in areas of steep noise gradients, such as near the ends of barriers. Furthermore, users should avoid encompassing an entire TNM run with a contour zone.

    To compute a contour zone about a barrier/roadway, create a contour zone in front of the barrier/roadway and behind the barrier/roadway.

  4. How do I workaround an "NMPlot Out of Memory" error?

    If your computer displays an "Out of Memory" error while running NMPlot, modify your computer's memory allocation for MS-DOS applications as follows: open an MS-DOS window; select the MS-DOS window's upper-left icon; select Properties in the resultant pull-down menu; select the Memory tab; then increase the values shown. For Windows NT and Window 2000, this step is not necessary since memory allocation is handled automatically by the operating system.

  5. How do I workaround an NMPlot "run-time 200" error in TNM previous to Version 2.0?

    The original version of NMPlot included in the TNM package was having difficulties running on today's fast computers (typically faster than 200 MHz) giving some users a runtime error message. Users should download the newer DOS version of NMPLOT, Version 3.06, which corrects this error. To use Version 3.06, replace the existing NMPLOTX.EXE file located in your TNM/PROGRAM/NMPLOT directory with the new executable file. NMPLOT version 3.06 is released with TNM versions 1.1 and above.

  6. How do I workaround a NMPlot "run-time 216" error?

    NMPlot may be experiencing difficulties handling large coordinates systems (coordinates in the millions). Try scaling down all the coordinates in your run. For example, if all your coordinates are 12,7xx,xxx.xx, then scale them down to 7xx,xxx.xx.

  7. How do I workaround a "Noisemap grid file could not be opened" error?

    NMPlot is a DOS application with an 8-character filename/directory limit. If your TNM run name is greater than 8 characters or is embedded within many subdirectories or has long subdirectory names, then NMPlot may display this error. Shorten your run name or move your run out to the main C: directory to run contours.

  8. How do I obtain contours to run in TNM Version 1.1?

    (Applies to TNM version 1.1 only)
    Some TNM 1.1 users are experiencing problems computing contours. Use TNM Version 1.0b or TNM 2.0 (or later versions) to generate contours.

  9. Why does TNM require a barrier in my run in order to run contours?

    You must select a "Remembered" barrier analysis prior to continuing on to calculating contours. A Remembered barrier design is required because TNM needs to know what sound level results to compute contours for since contour calculations will not be computed for all barrier designs, i.e., all perturbation-height combinations. Refer to Sections 10 and 12 in the TNM User's Guide for more information.

  10. How do I run contours without a barrier?

    To obtain contours for a "no barrier" case, create a "dummy" barrier with no height, create a barrier analysis, and then use Remember As to save the "dummy" design.

  11. When will the contour module be updated?

    Development is underway to implement the Windows version of NMPlot (Version 4.7) into TNM. In the interim, for users who would like to use some of the additional features that can be found in the Windows Version of NMPlot, it is available on the NMPlot website. To use Version 4.7, download and run install_nmplot.exe. Note that the contours viewed using NMPlot Version 4.7 will be external to TNM.

  12. Why do contours take so long to run?

    Based on user-input parameters, TNM generates a grid and interpolates the ground elevation at all grid points within the user-defined contour zone. If the user inputs a large contour zone and a very small contour precision, TNM will require a longer time to generate and interpolate those grid points. It is recommended that you carefully consider the size and tolerance of the desired contour zone area prior to calculating contours.

  13. I developed a noise reduction contour and saved the contour set with an extension of ".nrc", but when I try to load the contour set, TNM asks for a file with extensions of ".slc", ".idc", or ".ilc". How do I open the previously save contour set?

    This is a bug in TNM. To open your previously saved contour set, type in the full name of your contour set with the ".nrc" extension. If you cannot remember the full name of the contour set, the actual contour set file is located in the same folder as your TNM run.

  14. Are there specific objects that need to be present when producing contours?

    To produce contours, you must have at least one TNM Roadway, Receiver and Barrier anywhere within the run. The receiver and barrier do not need to be in the vicinity of where you want contours. You must also have a "barrier design." To create a barrier design, select your desired barrier and receivers with the mouse, and then click on Barrier Analysis->New. A new "Barrier View" will open. If you want the contours to be generated for a barrier set at the input height, then click on Barrier Analysis->Remember As. Here you can type in a name for your barrier design, click OK and it is saved. You can then exit out of the "Barrier View," select the contour you wish to calculate, and click on Contours->Define Contour Levels. Input your contour level data and then click on Contours -> Calculate. You will now be prompted to select a barrier design, and the one you just created will be included in the list. Select it and contours will begin calculating. If there are no other problems with the run, this will generate contours for your run.

    To calculate open field contours, create a "dummy" barrier by using zero as the height of the barrier. The barrier does not need to be in the open field, but if it is, remember that its Z-ground defines the ground elevation and thus will affect the contour. Also, you must have at least initiated a Barrier Analysis and have a "remembered" design to choose for the contouring, even if it is a no-height barrier. You do not have to have calculated the sound levels at your regular receivers, however

  15. What contour tolerance should I use in TNM?

    Typically, use 1 dB. However, some Users have used larger tolerances for specific project-related purposes.

  16. What is the minimum grid spacing that should be used when computing contours?

    Do not use the default of 61 m (200 ft), which is too large. Use very small grid spacing, such as 1.52 meters (5 ft.), for runs with rapid sound level changes (near barriers, for example). Larger spacing, such as 15.24 meters (50 ft.), can give incorrect results near barriers.

  17. What grid height should I use when computing contours?

    Typically, use 1.52 meters (5 ft). However, make sure your contour zone is big enough to encompass all relevant user-input ground elevations, which TNM uses to compute the ground elevations of contour grid points.

  18. Is there a character limit when naming Grid Files and contour sets?

    Since the current version of NMPlot used by TNM is a DOS program, your Grid File must satisfy DOS's maximum of 8.3 characters and DOS's restriction against some characters (such as "spaces"). For example, 12345678.123 is a valid file name. This limit means you are very constrained because a given grid file is for a specific contour zone with a specific set of values for tolerance, spacing and height for a specific barrier design in a specific TNM run. It is essential to keep a log of the grid file names and the related conditions that they represent.

    Keep in mind that changing the size of a contour zone does not invalidate a previously computed grid file, even though the calculated contours can be affected by being close to the borders of the contour zone. Also, changing the geometry of other TNM objects does not invalidate a grid file for a given TNM run (even when adding terrain points that obviously will change the sound levels). Such changes do invalidate results at the user-input receivers, however.

  19. Why do the calculated contour lines seem to intersect one another and give separate sound level results?

    Sometimes contour lines can intersect one another within a given contour zone and give separate sound level results. This is caused by ending the contour zone too close to where the sound level is rapidly changing. Do not end the contour zone near barrier ends, building row ends, or roadway ends. This can also happen when the grid spacing is too large.

  20. Can I encompass my entire TNM run with a noise contour?

    It is recommended that users do not encompass an entire TNM run with a noise contour. While contour zones can intersect other TNM objects, users should be advised not to intersect or encompass roadways and barriers with contour zones, because contouring logic can break down in areas of steep noise gradients, such as near the ends of barriers.

  21. I'm using Version 1.0b to calculate contours but NMPlot says that the contour settings were either too high or too low. What does that mean?

    (Applies to TNM version 1.0b only)
    During a contour sound level calculation, an NMPlot error may show up in your computer task bar and read,

    "All contour levels are set either too high or too low. No contours will be generated. Would you like the have new contour levels automatically calculated?"

    Disregard this message. It is a bug in NMPlot itself and does NOT affect the acoustics. Click "Yes" and the contour will complete its calculations.

  22. After calculating contours, the contour lines are displayed but no text is displayed for any object in the view. What is causing this?

    The contour has not been fully calculated, therefore not displaying any results. There may be some intersecting roadways or other objects that are interfering with your contour calculation. Please send your case to support@trafficnoisemodel.org and we will investigate it. Zooming in and then zooming out or minimizing the plan view window and maximizing it may show the contour levels (if they were calculated).

    This can also mean that in your other views, the labeling of text/point numbers is missing. But they are there - you're computer just doesn't know how to display them. 1) Ensure that the desired items are checked in the Show/Hide dialog, which can be accessed using the View menu; and (2) refer to Section 6.2 in the User's Guide and Section 2.3.1 in the User's Guide Addendum for more information on how to manually tell your computer how to display text.

Updated: 07/15/2011
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